Currently we heavily rely on bash in our tox.ini:

• cover.sh (Removing cover.sh and folding into tox config. #1237)
• custom_pip_install.sh (Removing use of wheelhouse and relying on Travis caching. #1350)
• merge.sh (Removing merge.sh. #1364 Only run from .travis.yml, no longer needed after Removing use of wheelhouse and relying on Travis caching. #1350 is in since merge.sh only delegates to update_docs.sh after the fact)
• pep8_on_repo.sh (Updating lint tox rule #1348)
• run_system_tests.sh (Move system test runner from bash to Python #1349)
• update_docs.sh (Only run from merge.sh)
• update_wheels_project.sh (Removing use of wheelhouse and relying on Travis caching. #1350)
• Makefile

We could do this by re-thinking those commands and just using shell-agnostic commands in tox.ini or we could get someone who knows Windows well to write a PowerShell equivalent for us.

A nice tox tricks and patterns post suggests using a foo.cmd file and then

#!/bin/bash -eE

:<<"::batch"
@echo off
powershell -ExecutionPolicy ByPass -File foo.ps1 %*
goto :end
::batch

foo.sh $*
exit $?

:<<"::done"
:end
::done

where foo.ps1 is PowerShell and foo.sh is bash.

This way the ::batch heredoc gets run on Windows and skips over the foo.sh part via goto :end, while on *nix systems the ::done heredoc is skipped due to the exit $?

UPDATE: I wasn't sure what the : did before the heredocs but I see that it acts as a way to comment them out in bash. This helps explain the Windows side of things; the lines starting with : and :: are ignored, but those with : can be jumped to while the others can't.